Earthling

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Main features in earthing

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Earthling

  1. 1. Earthing<br />G.V. Nilanka<br />
  2. 2. Content………..<br />purpose of earthing<br />Earthing design<br />Soil resistivity testing<br />Resistance to earth of a rod or pipe electrode<br />Resistance to earth of a strip<br />Resistance to earth of a infill material<br />
  3. 3. purpose of earthing<br />We provide a direct path to fault current.<br />What is fault current?<br />By earthing we can get common reference potential in electrical system.<br />There are several earthing arrangement<br />To achieve good earthing,a suitable low resistance to earth is desirable.<br />
  4. 4. Earthing design <br />Using Rods or pipe<br />Using Strip <br />Using Infill material<br />Using foundation<br />
  5. 5. Soil resistivity testing<br />This varies with some parameters.<br /><ul><li>moisture content
  6. 6. temperature
  7. 7. Depth </li></li></ul><li>Soil resistivity testing<br />
  8. 8. Calculate the soil resistivity<br />ρ=2πAd<br />ρ=soil resistivity<br />A=Apperant resistance<br />D=distance between adjacent electrode<br />
  9. 9. Resistance to earth a rod or pipe electrode<br /> R=ρ(ln(8l/D)-1)/2πL<br />L =length of electrode<br />D=diameter<br />ρ = resistivity of soil<br />
  10. 10. Cont….<br />l varies with electrode arrangement<br />
  11. 11. Three types of copper rods are commonly available. <br /><ul><li> Solid Copper
  12. 12. Copper clad steel rod ( copper shrunk onto the core)
  13. 13. Copper Bonded steel core (copper is molecularly bonded to nickel plated steel rod) </li></li></ul><li>Resistance to earth of a strip<br />L – length of the strip <br />h - the depth buried <br />w - width of the strip<br />P and Q are coefficient for strip or round conductor<br />Rn=FR<br />
  14. 14. Resistance to earth of a infill material<br />Where<br />ρ = resistivity of soil in Ω-m <br />ρc = resistivity of infill material Ω-m <br />d = Diameter of the electrode – m <br />D = Diameter of infill – m <br />L = Driven Length – m <br />
  15. 15. Thank You<br />

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